The role of cyclic AMP in hormone-induced lipolysis in fat cells has been well established. However the role of cyclic GMP in hormone-induced lipolysis is not clear. We have studied the effect of various hormones on cyclic GMP as well as cyclic AMP levels in isolated fat cells. Epinephrine and acetyl choline causes a marked increase in cyclic GMP in fat cells within seconds while cyclic AMP level was increased by epinephrine more slowly. The early increase of cyclic GMP was potentiated by Propranolol, a beta adrenergic blocking agent, while the later increase in cyclic GMP was blocked by phentolamine, an alpha adrenergic blocking agent, indicating that an adrenergic mechanism may be involved in cyclic GMP increase in the fat cell. The role of cyclic GMP in hormone-induced lipolysis is not yet clearly understood. It may have a modulatory role on hormone-induced lipolysis.